H-Bonding Additives Act Like Lewis Acid Catalysts

Schreiner, Peter R.; Wittkopp, Alexander

doi:10.1021/ol017117s

Cited by 454 publications

(257 citation statements)

References 29 publications

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“…Based on the results of the reported thioureacatalyzed reactions, [10][11][12][13][14] a variety of bifunctional amino thioureas such as 2a-c were designed by replacing one of the aryl rings of diaryl thiourea 1 by cyclic and acyclic 2-(N,N-dimethylamino)ethane derivatives as a chiral scaffold. To compare the reactivity and selectivity between thiourea and amide, bifunctional amide 2d was also prepared (Fig.…”

Section: )mentioning

confidence: 99%

“…Recently, hydrogen-bond donors such as ureas/thioureas, [10][11][12][13][14][15][16][17][18][19][20][21][22][23] BINOL/diols, [24][25][26][27][28][29][30][31][32] and phosphoric acids [33][34][35][36][37][38][39][40] have been also recognized as efficient organocatalysts. Novel urea and thiourea derivatives were developed as organocatalysts and their potential as a general acid has been successfully demonstrated by several groups.…”

Section: Introductionmentioning

confidence: 99%

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Development of Chiral Thiourea Catalysts and Its Application to Asymmetric Catalytic Reactions

2010

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We have developed several multifunctional thiourea catalysts bearing a tertiary amine or an 1,2-amino alcohol in expectation of their synchronous activation of a nucleophile and an electrophile through both acid-base and hydrogen-bonding interactions. From these studies, it was revealed that the weak acidity of thioureas compared with metallic Lewis acids could be overcome by this modification. The bifunctional aminothiourea could be used efficiently for a wide range of diastereoselective and enantioselective nucleophilic reactions such as Michael addition of 1,3-dicarbonyl compounds to nitroolefines, aza-Henry reaction of nitroalkanes to N-Boc imines, and hydrazination of cyclic b b-keto esters. We also discovered that multifunctional thiourea catalyst, bearing an 1,2-amino alcohol moiety, significantly accelerated the Petasis-type reaction of alkenylboronic acids to Nphenoxycarbonyl quinolinium salts, prepared from quinolines and phenyl chloroformate, to afford 1,2-addition products with high enantioselectivity (up to 97% ee). Furthermore, to expand the synthetic applicability of the thiourea-catalyzed asymmetric reactions, tandem organocatalyzed reactions were explored to establish the concise one-pot synthesis of chiral densely functionalized three-, five-, and six-membered compounds.

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Section: )mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Development of Chiral Thiourea Catalysts and Its Application to Asymmetric Catalytic Reactions

2010

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“…For example, Schreiner has employed a thiourea (25 mol % loading) to activate oxazolidinones (complex I, Figure 1) for Diels-Alder reactions. [4] Philp has shown that a diamidopyridine (100 mol %) activates maleimide (complex II, Figure 1) for 1,3-dipolar cycloadditions. [5] Göbel reported that amidinium ions (25 -100 mol %) were capable of activating 1,2-diketones (complex III, Figure 1) for Diels-Alder reactions, [6] and a sulfonamide has been used to accelerate the addition of pyrrolidine to 2(5H)-furanone, presumably via complex IV (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Planar Chiral PHANOLs as Double Hydrogen Bonding Donor Organocatalysts: Synthesis and Catalysis

2004

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Abstract:4,12-Dihydroxy[2.2]paracyclophanediol (PHANOL; 1), and its para-substituted derivatives 2, 5 and 7, were found to catalyse Diels-Alder cycloadditions of a,b-unsaturated aldehydes or ketones with dienes and/or epoxide ring opening reactions with amines. The mode of catalysis by the PHANOLs is via double hydrogen bonding to the two sp 2 lone pairs of a carbonyl group or the two lone pairs of the epoxide. The order of activity of the PHANOLs for catalysis of the Diels-Alder reaction essentially correlates with the expected hydrogen-bond donor strength based on the degree of electron-withdrawing capability of the group(s) in the para position. In contrast, ortho-substituted PHANOLs 10, 11 and 14 were not active as catalysts due to steric interference with the double hydrogen bonding mode. 1 H NMR and IR spectral data for the various PHANOLs are discussed in support of the proposed double hydrogen bond mode.

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“…Thus, various carbonyl group reactions catalyzed by urea or thiourea compounds have been developed. [15][16][17][18][19][20][21][22] At the outset of our studies for developing new chiral urea and/or thiourea catalyst of the hetero-Micahel reaction, we investigated the reaction of pyrrolidine (2) with g-crotonolactone (3) in the presence of the simple ureas 5 and 7, 17) thioureas 6 and 8, 17) and guanidine 9 as catalysts (Fig. 2).…”

Section: Resultsmentioning

confidence: 99%

Development of Novel Chiral Urea Catalysts for the Hetero-Michael Reaction

et al. 2004

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Michael addition to a,b-unsaturated carbonyl compounds is one of the fundamental bond-forming processes and offers an extremely powerful tool for the synthesis of highly functionalized organic molecules.1) Thus, development of efficient chiral catalysts for this reaction is still an exciting topic in synthetic organic chemistry.2,3) Various types of catalysts have been developed so far. Among them, organocatalysts are especially attractive since they do not require strictly controlled reaction conditions, and are not considered to have much unfavorable environment effect compared to the metalcontaining catalysts. 4,5) We have recently developed the novel C 2 -symmetrical chiral cyclic guanidine compounds 1 as new organocatalysts, 6-9) whose structure was inspired by the marine guanidine alkaloid ptilomycalin A 10-12) and its analogs (Fig. 1). 13,14) These catalysts were found to accelerate the heteroMichael reaction depending upon their cavity size. 7) One of the catalyst 1b works as phase-transfer catalyst for the alkylation of Schiff base imine with high enantioselectivity.8) Although 1 possesses wide possibility to be developed as superior organocatalyst, it also have some deficiencies, i.e., requirement for relatively long steps preparation, and no asymmetric induction at the hetero-Michael reaction.7) To overcome these issues, we focused our attention on urea and/or thiourea compounds, which can be grasped as core structure of 1, as prototype of new efficient and practical organocatalysts. Herein we wish to report the preliminary/basic results of a novel urea-type catalyst 10 for the hetero-Michael reaction, including results on an asymmetric version of this conjugate addition reaction. Results and DiscussionUrea and thiourea groups are known to coordinate to a carbonyl group as guanidine group, and to activate it by lowering the LUMO energy via partial protonation. Thus, various carbonyl group reactions catalyzed by urea or thiourea compounds have been developed. [15][16][17][18][19][20][21][22] At the outset of our studies for developing new chiral urea and/or thiourea catalyst of the hetero-Micahel reaction, we investigated the reaction of pyrrolidine (2) with g-crotonolactone (3) in the presence of the simple ureas 5 and 7, 17) thioureas 6 and 8, 17) and guanidine 9 as catalysts (Fig. 2).These reactions were performed under Mendoza's conditions, [23][24][25][26] i.e., the ratio of 2, 3 and catalyst was 1 : 1 : 0.1, and the concentrations of the substrate 2 and 3 were set at 0.3 M in CDCl 3 . The accelerating activities of the catalysts for this hetero-Michael reaction were determined by measuring the t 1/2 (monitored by 1 H-NMR), and the results are summarized in Table 1.The urea 5 and thiourea 6 accelerated this conjugate addition reaction 3.0 and 2.6-fold, respectively, over the uncatalyzed reaction as expected. From the consideration of the reaction mechanism (vide infra), introduction of EWGs on the aromatic rings of 5 and/or 6 was expected to increase their catalytic activity. In fact, catalysts 7 ...

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H-Bonding Additives Act Like Lewis Acid Catalysts

Cited by 454 publications

References 29 publications

Development of Chiral Thiourea Catalysts and Its Application to Asymmetric Catalytic Reactions

Development of Chiral Thiourea Catalysts and Its Application to Asymmetric Catalytic Reactions

Planar Chiral PHANOLs as Double Hydrogen Bonding Donor Organocatalysts: Synthesis and Catalysis

Development of Novel Chiral Urea Catalysts for the Hetero-Michael Reaction

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